Sustainable polyhydroxybutyrate production and characterization from Chlorella vulgaris cultivated on waste-derived carbon sources.

Polyhydroxybutyrate (PHB) is a biopolymer produced by various microorganisms for carbon and energy storage and stands out in terms of sustainable bioplastic production. PHB is a biodegradable and sustainable substitute for petrochemical-based plastics frequently used nowadays. Interest in waste-based/byproduct carbon sources has recently increased due to the high production cost of microbial PHB, and byproducts and wastes are being evaluated within the scope of zero-waste projects. In this study, the metabolic changes of Chlorella vulgaris were examined in the existence of different substrates including wine vinegar (WV), vinegar wastewater (VW), crude glycerol (CG), and tomato paste wastewater (TPW), and the effects of these conditions on PHB production were evaluated. Changes in cell dry weight, optical density, pH, total reducing sugars, total -nitrogen, -carbohydrates, -proteins, -lipids, and PHB levels were monitored over time during cultivation. 1% (v/v) VW was found to be optimal carbon source/concentration. To optimize extraction, solvent-based and ultrasonic extraction methods were tested for different durations, and the highest yield of 23.280 ± 2.10% was determined after 15 days. The extracted PHB was characterized by FTIR, GC, NMR, TGA, DSC, and SEM analyses. Thus, the characteristic functional groups of PHB obtained from C. vulgaris have been confirmed. This study provides important data on directing carbon flow to PHB production metabolism in mixotrophic microalgal cultures using waste/byproduct-based carbon sources and demonstrates that the potential of C. vulgaris in bioplastic production can be revealed through metabolic and nutritional optimizations.